building a new kernel

I am not new in BSD and I know how to compile a new kernel for FreeBSD
or NetBSD...

But it is the first time I download the source using cvsup. And, all
the files, being in /home/dcvs/, are ending with ",v"
Why?
If I copy all the source files in /usr/src/, I cannot build a new kernel...
What have I to do after downloading the source via cvsup?